<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function calc(){
            var a = parseFloat(prompt("请输入第一个数字："))
            var b = prompt("请输入+、-、*、/")
            var c = parseFloat(prompt("请输入第二个数字："))
            var s = 0
            switch(b){
                case "+":
                    s= a +c
                    break
                case "-":
                    s= a - c
                    break
                case "*":
                    s= a*c
                    break
                case "/":
                    s=a/c
                    break 
            }
            alert("和为" +s)
        }
    </script>
</body>
</html>